Automatic telephone system



April 30, 1929. T. F. CROCKER AUTOMATIC TELEPHONE SYSTEM 2 sheets-shed 1 Filed June 24, 1927 ThnmasF Bruckn- April 30, 1929. "r. F. CROCKER AUTOMATIC TELEPHONE SYSTEM Filed June 24, 1927 2 Sheetg-Sheet 2 saw I 5% .a\\ IL Imren nr' Thomas F Cracker Patented Apr. 30, 1929.

THOMAS Fw CROCKER, OF CHICAGO, ILLINOIS, ASSIGNOR TO RESERVE HOLDING COM- PANY, on KANSAS CITY, i rxssounr, A CORPORATION or DELAWARE.

AUTOMATIC TELEPHONE SYSTEM.

Application filed June 24,

This invention pertains to automatic telephone systems in general, but is more particularly concerned with telephone systems in which calls extended to dead or unequipped selector levels or to unequipped connector bank contact sets are automatically trunlred to an intercepting operator. The objectof the inrention is the provision of new and improved trunk circuits for the trunks extending to the intercepting operators position, and the provision of a new and improved intercepting opcrators cord circuit for answering intercepted calls.

In an automatic telephone system of this kind in which intercepting service is provided, if a calling subscriber or a toll operator in attempting to set up a connection to a called subscriber dials. a wrong digit, and as a result causes the automatic switch operated thereby to operate to an unequipped lerel, or to an uncquipped set of bank contacts, the call will be t-runked to the intercepting operator, The inter cepting operator will then answer the call and inform the calling subscriber or the toll operator of the mistake, and also give him such information as she may have concerning the wanted subscriber.

Most commonly, in automatic telephone practice the toll operator sets up toll connections by dialing the directory number of the called subscriber, causing one or more selecors, one of which is termed a toll transrri 'on selector, and a conni-uator to successively operate and extend the connection to the called line. ii the called line is busy, the operator recciwe the busy tone, but it the 'die, a supervisory lamp at her to apprise her that the in telephone practice, it le that the operations perthe toll operator and the supern be uniform, regardless of whether she has obtained connection with w riled subscriber or has dialed a wrong nib r a d has obtained connection with eptirg operator.

v feature oi? this invention 1 1 .tion of intercepting trunk cirfor the trunlcs mztcndiug from the uncouipped selector levels, from the racant toll emission "elector levels, and iflfOlll the 1 nl: contact sets of the conuhug to the intercepting operathe characteristic of each of th being 1927. Serial No. 201,143.

such that when a "all is extended thereto, the toll operator receives the same signals as though she had completed the connection to the wanted subscriber.

Another important feature of this invention resides in the new intercepting operators cord circuit. are contained means for tripping the ring which functions when the operator inserts the plug of the cord into the jack of a trunk from unequipped connector bank contact sets to answer a call extended thereorer, and which will refunction ii a second call is ex tended to this same trunk before the intercepting operator has rcniovedthe plug. lllhe ,ring tripping arrangement used is amodification of the arrangement disclosed in theapplication otV. S. Tharp Serial No. 136,925,1iled September 22, 1926.

In the following specificat on these features and others not specifically mentioned, and the operation thereof will be described in detail with the ,aid of the accompanying drawings comprising Figs. 1 and 2. llhese drawings illustrate by means of ,the usual schematic circuit diagrams the new and i111- pro'ved trunk circuits and intercepting operators cordcircuit introduced by this invention and also show diagrammatically the main switches ofan automatic ltelephone,systern, operated in the extension of a conneo tion from a toll operator-to it called subscriber, with which the trunk ciuguits are associated.

l'be drawings tobe most easily understood should be placed with Hg. 2 to the right of Fig 1, with the cor esponding lines in alignment in the up ierhalt ot ,lvit toll opcrutois cord circuitl) i rniiuati in the plug P and a ti'u 'ik accessible at jack J and terminating in the selector S is shown. As many of such cords and trunks are provided as are necessary to take care of the service. The operators cord circuit may beof any suitable type and is therefore not shown in full; only those clementswhich concern the o leration. of the invent on are shown. The

selector S may be of any suitable type, such as the well known vertical and rotary ty ie, having horizontal rows or levels,ofbanlrcon tacts. In the banl-zs of. this and other lectors in multiple in as many le rels as is required, trunk lines are accessibletoia number of groups of toll transmission selectors. The bank contact sets of the ,ul equipped In this new cord circuit levels, however, are multipled together and connected to one or more trunks extending to the intercepting operators position, such as the trunk comprising conductors 36, 37 and 38, terminating in the jack J", and hav ing the associated trunk circuit TC.

The intercepting operator is equipped with one or more cords such as a cord circuit 0, terminating in the plug P. The trunk circuit T G and the cord circuit 0 form a particular part of this invention and will be de scribed in detail subsequently.

The trunk line com iirising conductors 36, 37 and 38, and accessible at the bank contacts 6, 7 and 8 of the selector S, terminati-is in the toll transmission selector Eli. The toll transmission selector El shown only in skeleton, may be of any suitable type, but for descriptive purposes it is assumed to be like the one disclosed and described in detail in the Patent #1,G33,1d9, granted to John Nicks, June 21, 1927. In a number of levels in the banks of this and other similar toll transmission selectors in multiple, access is had to a corresponding number of groups of connectors. The bank contact sets of the unequipped levels out the toll t ansmission selectors, however, are multiply connected to one or more intercepting trunks extending to the intercepting operators position, such as the trunk comprised in conductors 136' to 139, inclusive, terminating in the jack J and having the associated trunk circuit T0 The trunk circuit TC forms a particular part of this invention and will be described in detail subsequently.

The trunk comprising conductors 136 to 139 inclusive and accessible at bank contacts 16 to 19 inclusive terminates in the connector H. The connector H, shown only in skeleton, may be of any suitable type but again for descriptive purposes it is sumed to be like the one disclosed and described in detail in the above referred to patent. In its banks, the connector H together with other similar connectors and also with other local connectors (by which local subscriber to subscriber connections are completed) has access to subscribers lines, such as the line extending to substation A. The unequipped connector bank contact sets, however, are multiply connected to one or more trunks extending to the intercepting operators position, such as the trunk comprising conductors 2 .36, 237 and 238, terminating in the jack J", and having the associated trunk circuit TC With this general description of the objcct of the invention and the apparatus involved in mind, a detailed description of the operation will now be given.

For this purpose, it will be assumed that the toll operator wishes to extend a connection to the subscriber at substation A. The general operations involved in setting up a toll connection from a toll operator to a called subscriber are well known, and there fore will be described in a more or less cursory manner. Detailed descriptions of these operations, however, are given in the above referred to patent. To extend a connection to the substation A the toll operator inserts the plug of an idle cord, such the plug P of the cord circuit O, into the jack of an idle trunk such as the jack J, (the idle condition of the trunk being indicated in any well known manner) and then throws the key ill to the left and operates the dial D in accordance with the directory nun'iber oil the subscriber at substation A. Responsive to the dialing of the first di it, the selector to operates to raise its wipers opposite the corresponding level of bank contat and. then automatically selects an idle trunk in this level. It may be assumed that the trunk comprising conductors 36, and l no is the one selected. Responsive to the dialing of the second digit, the toll transmission tor EF operates to raise its wipers opposite the corresponding level of bank contacts and then selects an idle trunk accessible therein. It may be assumed that a trunk line comprising conductors 136 to 189, inclusive, tern1ihating in the connector H is the one selected. When this trunk is seized, in addition to the line relay 201 and the release relay (not shown) of the connector operating, the ring cut-oil relay 208 is operated and is locked to the ring control conductor 139. Responsive to the dialing of the next digit of the number the connector H operates and raises its wipers opposite the corresponding level of bank contacts, and responsive to the dialing of the last digit the connector ll rotates its wipers into engagement with the of bank contacts terminating the called line. Attcr completing dialing, the toll operator again restores the key K.

It the called line busy at this time the connector ll functions to connect the busy tone to the talking conductors and tin-thermore lamp L remains dark. The toll operator on hearing the busy tone (it she still has her listening key thrown) and noting the dark condition of the lamp L is informed that the subscriber at substation it busy, whereupon she will release the connection and try again at some later time. If the called subscribefis line is idle at this time, the current flow over the talking conductors 136 and 138 and supplied through the winding or line relay 201 is reversed (by the operation of relay 208). This reversal of current over these conductors causes the operation oi? polarized relay 103 in the toll transn'iission selector EF, which locks itself operated and reverses the current flow over the talking conductors 36 and 38, and through the polarized relay 10 in the operators cord circuit C). .thS a result relay 10 operates and closes the circuit of lamp L. The 1i ghtltll) lit! ill

ing of the lamp L indicates to the toll operator that the connection has been completed and that the line is idle. (The operation of polarized relay 103 also connects ground and battery to conductors 136 and 137 through the windings of relay 102 in direct opposition to ground and battery connections through the windings of line relay 201. This can s relay 201 to deenergize and close the c.' cuit of relay 200. Relay 200, in operng, prepares the circuits for signalling. r: mailing prevented for the present, since relay 208 is operated.)

When the toll operator is ready to signal the called subscriber, she will throw the key it. momentarily to the right, thereby applying ringing current to the trunk conductors 9J6 and 38 momentarily. As a result ringing relay 1% in. the toll transmission selector llll? operates and causes the operation of relay 101 which in turn disconnects ground cntial from the ringing conductor 39 conul to conductor 139. This causes the release of the ring cut-off relay 208 in the connector H, as a result of which ringing current is intermittently applied to the called line in the usual manner.

When the called subscriber answers, the ring cut-oil relay in connector H again operates and disconnects the ringing current from the called line. Furthermore, relay 102 in the toll transmission selector EF also operates over the called line loop and disconnects ground and battery from the trunk conductors 36 and 38. By reason of the interruption of current flow in the polarized relay 10, this relay again deenerglass and causes the extinguishing of the lamp L. The extinguishing of the lamp L at this time indicates to the toll operator that the called subscriber has answered whereupon the toll operator atter informing him that he is wanted in a toll connection pernut ccnwrsation to take place.

l' in the subscriber at substation A rehis receiver at the completion of the ration, relay 102 deenergizes and re- 10 in the operators cord again operates ind causes lamp L to light. The toll opcrator, noting this, releases the connection in the well known manner.

In the abovedescriptions, it was assumed that the toll operator dialed the correct digit in each instance, and obtained connection with the described subscriber. Should the toll operator, however, nlisdial any one of its. the call will be trunlred to the inopciator (providing of course she not obtain connection with some other ricer). The operations which result from the inisr' ialing of each of the digitsof a called number will now be described.

will first be assumed that the toll operafter having extended a connection by way of selector S and toll transmission selector EFto connector H, misdials one of the last two digits such that the Wipers are positioned on an nncquipped set of bank contacts connected tothe trunk line comprising conductors 236 to 23 8, inclusive. Finding this trunk idle, the connector H functions in the same way as when operated to connect with an idle line and reverses the flow of current over the trunk conductors 1.36 and 138, which finally results in the operation of the polarized relay 10 in the operators cord circuit as previously described. Again lamp L lights, indicating that a connection has been completed. lVhen the operator wishes to signal she again operates key K to the right momentarily. As a result the connector H functions to connect ringing current to the trunk conductors 236. and 5238' intermittently in the regular manncr. Responsive to the ringing current, relay 153 of the trunk circuit TC operates, locking up mechanically to the armatureof iIplay 152, and closing the circuit of lamp.

On perceiving the lighted condition of the lamp L the intercepting operator will insert the plug P? of the cord circuit 0 into. the jack J and will then operate the listening key K. It the operator inserts the plug in the jack during a ringing period, relay 54 is operated by the ringing current and by separating contacts 65 prevents any further operation from taking place. At the commencement of the next silent period, relay 54 deenergizes and by permitting con tacts 65 to close completes a circuit for relay 51 in series with relay 152. Relay 152, in operating, unlocks the mechanical lock holding relay 153 operated, and by separating contacts openstheringing bridge across the talking conductors. Relay 153, in releasing its armature, separates contacts 156 and opens the circuit oil lamp If.

Relay 51 of the cord circuit being onergized in series with rclayfllhfl, connects ground potential to the upper and.lowcrterminals of the impedance coil 50. As a result the ring cut-ofl relay 200 in the conncctm' H energizes and disconnects the ringing current from the trunk conductors and completes points in the talking connection. By the closure of contacts a circuit estab lished for relay :53. Relay operates and opens points in the talking leads 0). the cord circuit at contacts 62 and 6%, and by closing contacts 63 closes the circuit of relay Relay .52 operates in parallel with relay 51 and by closing contacts .58 and 01 closes points in the talkinglcads oi" the cord cir' cuit. By the closure of contacts relay establishes a locking circuit for itself independent of relay .53, and by separating con t acts 59the circuit of relay 51 is opened. Relay 51 now deenergizes and disconnects ground vfrom the terminals of the impedance coil 50 by separating contacts 57, and opens the circuit of relay 53 by separating contacts 55. Relay 53 thereupon falls back and opens the initial circuit of relay 52 by separating contact 63 and by permitting contacts (32 and G l to close again closes points in l'ltlllllll' leads of the cord circuit so that the intercepting operators head may now be connected across the trunk conductors. The purpose of the foregoing operations to prevent a talking circuit from being completed to the intercepting operatcis h. l set, should she have the listening key K thrown, until the ring has been tripped to prevent her from receiving disagriarablc noises in her car as would he produced when the ring was being trippei'l it her lhad set were connected across the line at 1 time.

After ground is disconnected lioin the terminals of the in'ipedance 50, r lay 102 in the toll transmission selector operates over the loop including impedance GO and resistances R and R in series and as before, by disconnecting ground and battery from the trunk conductors 36 and 38, causes rela 10 in the toll operatofis cord to release and extinguish the lamp L. This informs her that the extended call has been answered, whereupon she will operate her hey K, it it is not already operated, with the intention of informing the called subscriber that he is wanted in a toll connection. Instead, however, the intercepting operator will answer and inform the toll operator that she has dia ed the wrong number and give her such information as she may have concern ing the called subscriber.

Should the intercepting operator need to look up some matter for the toll operator, she may do so, and can rellash the toll operator by operating the flash key K" intermittently when she wishes to recall the toll operator. This opens and closes the circuit oi relay 102 in the toll transmission selector l ll which causes lamp L to flash.

After receiving this information the toll operator will remove her plug P from t jack J, and the intercepting operator will remove the plug P from the jack .l, thus causing the release of the connector in the usual manner. Removing the plug P {111331 the jack J also opens the circuit of relay 52 of the cord circuit 0 and relay or the trunk circuit TC" whereupon th sc relays restore to normal.

As previously described, the banks of the toll connector H are multipled with those of other local connectors, which are a icssible to other local subscribers for completing regular local connections. Therefore, should a regular subscriber, in attempting to establish a connection with the subscriber at substation A, dial a wrong number he may also obtain connection with the trunk line comprising conductors 236 to 238, inclusive.

In such a case, the intercepting operator would answer the call by inserting the plug P into the jack J in the same manner as described above. lVhen such a call is answered, the ring cut-elf relay of the regular connector (not. shown) over which the connection extended is operated by the closure of contacts 57 by the operation of relay 51 (the back bridge relay ol the cram-actor being prevented from o 'icrating winding of the back bridge relay connected to ground is shunted). Alter relay 51 deenergizes and opens contact 5?, the hack bridge relay is still prevented from oper ating by reason oil? the combined resistance ol coil 50 and resistances ll and ll limiting the current flow to too low a value However, as described above, the battery teed relays, such as relay 102, oi the toll transmission seleciors are; adjusted to operate in series with impedance 50 and resistances R and R Since the back-bridge relay ot' a local connector is not operated when a call extended to, and answered by, the interce iting operator (to prevent a local subscriber from being charged for such a call), a connection o'lf this kind is released as soon as the local subscriber replaces his receiver. Since this places the intercepting trunk used in an idle condition immediately, it is quite possible for another connection to be extended to this same trunk before the intercepting operator has removed the plug P from the jack J ol the trunk. According to a particular feature oil? this invention the ring will be tripped, nevertheless, and the intercepting operator may answer this second call without removing the plug from the jack. To describe this feature, it will be assiuned that before the intercepting operator removes the plug P from the jack J tLIltQl' answering one call over this trunk from a local subscriber another connection extended to this same trunk. Relay 5st again operates from ringing current (applied to the trunk conductors by the connector used in the second connection) and opens the circuit including relay 52 and 152 in series. lelay 152 in deenergizing again closes the ringing bridge in cluding ringing relay 153 across the trunk conductors. Therefore, relay 158 is again operated by ringing current and the lamp L is lighted.

At the end of the ringing period in which relay o-l was operated, relay 54L releases and in so doing, permits relays 51, 53 and 52 to operate and trip the ring and close the talking circuit to the intercepting opcratocs head set as previously described. Relay 152 in operating (first in series with relay 51 and then in series with relay 52) again opens the ringing bridge across the trunk conductors, causing relay 153 to deenergize and extinguish the lamp L.

since the Y lll) lit)

Cir

The second lighting of lamp L is of course more or less in the nature of a flash; but the intercepting operator is not wholly dependent upon the perception of this flash to indicate to. her that a second connection has been extended. During the instant after ringing current is applied to the trunk conductors and before relay 5?. is released by the operation of relay 54., ringing current passe. through the intercepting operators head set, giving her a decided click, which is further indication that a second connection has been extended to her. She may answer this second connection as she did the first without any further procedure.

To further describe the invention, it will be assumed that thetoll operator in attempting to extend a connection to a called subscriber up a conne' on through selcctor to the toll transmission selector Eli,

and then makes a mistake in the next digit and as a result causes the toll transmission selector El to extend the connection to the intercepting operator over the trunk comprising conductors 136" to 139 inclusive. lVhen this trunk is connected with, ground potential is connected to both the regular release conductor 137 and the ring control conductor 1S9. relay 104: is energized from ground on conductor 137, the circuit including contacts 106 and contacts 109, and in operating opens a point in the circult of the lamp L at contacts 112, opens a point in the ring-back tone circuit by separating contacts 115, closes the circuit for relay 103 by closing contacts 114, and closes a locking circuit for itself at contact LL13 in series with relay 105 and the ring control conductor 139. Relay 103 operates and closes point in the circuit of lamp l at contac S, closes a point in the ring l" "l; tone circuit atcontacts 111, opens a or Ant in the initial energizing circuit of relay ltll by separating contacts 109, and by tiles f independent of relay 10st. Re i" y 1011', in energizing, connects ground and tttery potential through protecting resistances to the upper and lower talking conductors of the trunk line respectively. As a ult, polarized relay 103 in the toll trausm on selector El operates and locks and rere the direction of current flow over the trunk (aiuductors 36 and 38. The operator, however, not knowing that she has obtained connection with a trunk line leading to the intercepting operators position continues to dial, but further dialing has no ellhet. hen she has completed the dialingshe restores the key If to normal. Polarized relay 10 now operates and causes lamp L to light. This normally indicates to the toll operator that the call has been or. i: eat d. 1

Again when the toll operator Wishes to contacts 110 closes a locking circuit a signal, she operates the key K to the right momentarily. As. a result, ringing relay 101 in the toll transmission selector EF operates and causes the removal of ground potential from the ringing control conductor 139, which now opens. the, locking circuit of relay 10 1 in series with relay 105. Relay 105 deenergizes and in restoring removes the battery and ground connections from the trunk conductors 136 and 138.

Relay 10-.l deenergizes and in sodoing, closes the circuit of lamp L at contacts 112, opens a point in its own locking circuitat contacts 113, opens the initial energizing circuit of relay 103 atcontacts 114, and closes the ring-back tone circuit atcontacts 115. The toll operator (if her key If is operated) hears the ring-back, tone, indieating that signalling is takingplace The lighting of the lamp L signals the intercepting operator. The intercepting operator answers the call b' inserting the plug P of the cord circuit into the jack .J As. a. result relay 102 operates over its lower winding in series with relay 51 of the. cord circuit 0'. Relay 102, in operating, closes a locking circuit over its upper winding and at the same time opens the locking circuit of relay 103'. Relay103 falls back and opens the circuit ofthelainp L at con:

tacts 108, opens a point in its ownlocking the lamp L] This signals the toll operator who then connects her head set to this trunk by operating key K, providing it is not already connected thereto. The intercepting operator answers and informs the toll operator of her mistake.

It should be noted that should tercepting operator answer immediately,

the inthat is, while thetoll operator still has the key K" thrown to the right, ringing current will be induced in the secondary windings of the repeating coil R of the toll transmission selector EF and cause the op eration of relay 54. The operation of relays 51, 52 and 53 is thus dela ed until after the ringing current ceases, and by preventing the completion of the talking connection. (should the key K. be operated) to the intercepting .operators head set, until after ringing current has ceased, the

- without ellect.

possibility of the operator receiving dis agreeable noises in her ear is eliminated.

After the toll operator has been informed of her mistake, she will remove the plug P from the jack J, and the intercepting operator will remove the plug P from the jack J, causing the release of the connection in the usual manner. Removing the plug P from the jack J also opens the circuit of relay 52 and relay 102. Relay restores and relay 102 likewise restores after the circuit oii its upper winding is opened upon the release of the toll transmission selector EF.

It should be noted that since relay 102 is locked up over its upper winding, this relay would not dcenergize until after the toll transmission selector El was released, should the intercepting operator be the first to withdraw her plug l? from the jaclr J.

This prevents a false reoperation o'l relays 103, 104; and 105 which would otherwise take place in such case.

To further describe the invention, it will be assumed that the toll operator after in sertin g the plug P into the jack J and throwing the key K to the dialling position, with the intention of extending a connection to some subscriber, dials the wrong first digit and as a result causes the selector S to extend the connection to the intercepting operator over the trunk comprising conductors 3'6, 3'7 and 38, terminating at the jack J. hen the connection is extended to this trunk line, line relay 73 of the trunk circuit TC operates and closes the circuit of release relay 741:. Release relay 74: operates and places ground potential on the release conductor 37 to maintain the selector S operated and mark the trunk busy. The line relay 73 energizes and deenergizes correspondingly responsive to thedialing of the remaining digits of the called number, but The circuit of relay 74, is opened each time relay 73 decnergizes, but

being slow to release relay 7% maintains its armature attracted mn'itimiously.

lVhen the toll operator has completed dialing, she restores the key K to normal. The current now pas cs through the winding of the polarized relay 10 from the bat tery supplied through the windings oi the line relay 73 of the trunk circuit TC, the direction being such as to cause this relay to operate and light the lamp L. Thus the operator is given the same indication as though the connection has been extended to the desired substation.

When the operator is ready to signal, she again operates key K to the right momentarily applying ringing current to the line conductors. This causes the operation of the ringing relay 72. Relay 72 locks itself to the armature of relay 71, mechanically, closes apoint in the ring-back tone circuit at contacts 80, and closes a circuit for the lamp L at contacts 79. "he tell operator hears the ring-back tone, providing she has her hey K operated. he lighting of the lamp L indicates to the intercepting operator that a call has been extended to her position.

The intercepting operator answers the call by inserting the plug P into the jack J and operating her listening key K (it it is not already operated). Inserting the plug P into thcjacl: J closes a circuit for relay 71 in series with relay 51.. Relay 71. operates and disconnects the lmttery teed relay 73 and also the ringing relay 72 from the trunk conductors at contacts 77 and T8, and closes another circuit for rel ay Tl: a l: contacts 76. In operating its armature. relay Tl unlocks the armature of relay 7 The restoration oil. the armature oi? relay .2 opens the circuit of the lamp L and opens the ringback tone circuit. Disconnecl'in the ha ti cry teed relay from the trunk conductors opens the circuit for the polarized relay 10 in the toll operators cord circuit. Relay 10, in restoring, extinguiv ms the lamp L, which signals the toll operator. The toll operator then connects her head set to this trunk and is then informed of her mistake by the intercepting operator.

Bitter receiving this information the toll operator removes the plug P from the jack J. and the intercepting operator removes the plug P from the jack J. The latter operation opens the circuit oit relay in series with relay 71, both of which restore to normal. Relay 74; likewise restores to normal atter its circuit is opened at contacts 76, and by removing ground from the conductor 87, permits the selector S to restore.

This QOIHPlQtQS the description oi the in rention. hat is thought to be new and is desired to have protected by Letters Patent is specifically stated in the appended claims.

hat is claimed is:

1. In a telephone S y l'CI11,2lll operatofs switchboard, a trunk terminating in a jack at said switchboard, means including a con nector switch tor extending a connection to said switch via said trunk, means in said connector including a ring cut-oil relay for ap nying ringing current to the coiuluctors of said trunk line aitcr said connection is extended, an operatofis cord terminating in a plug, and means in said cord re ponsive to the insertion of said plug into said jack to answer the cal and rcsponsi re to the extension of the connection providing said plug is in said jack at the time the connection is extended for operating said ring cut-oli relay.

2. In a telephone system, a trunk line. an operators cord adapted to be connected to said trunk line, means for establishing a. coin nect-ion to said trunk line and for applying iil ringing, current thereto, and means responsive to the connection of said cord to said trunk line to answer the call, and responsive to the establishment of said connection providing said cord is connected to said trunk line at the time the connection is established for tripping the ring.

3. In a telephone system, a trunk line, an operatofis cord adapted to be connected to said trunl: line, means for estahlishinp a connection to said trunk line and for apply-- lug ringing current thereto, means responsive to the connection oi said cord to said trunk line to answer the call, and responsive to the establishment of said connection providing said cord is connected to said trunk line at the time the connection is established, for tripping the ring, an ope 'ators head set normally t isconnccted from said cord, and means for automatically connecting said head set to said cord a moment after the ring is tripped.

l. In a telephone system, a trunk line, an operators cord adapted to be connected to said trunk line, 111 runs for extending calls to said trunk line and for applying ringing current thereto each time a call is extended, tripping means responsive to the connection of said cord to said trunk line to answer a all for tripping the ring, and means for causing said tripping means to reoperate providing a second call is extended to said trunk line before said cord is disconnected therefrom after answering the first call.

5. In a telephone system, a trunk line, an operators cord adapted to be connected to said trunk line, means for extending calls to said trunlr line and for applying ringing current thereto each time a call is extended, tripping means responsive to the connection of said cord to said trunk line to answer a all for tripping the ring, means for causing said tripping means to reoperatc providing a second call is extended to said trunk line before s id cord disconnected therefrom at'ter answering the first call, an operators head set normally disconnected from said cord, and means for automatically connectinp said head set to said cord a moment after each operation oi said tripping means, said means lacing deini-tuatcd when a second call crdeuded hy the means il or causing said tripping means to reoperate.

6. In a telephone system, a trunk line, an operators cord adapted to be connected to said trunk line, means for extending calls to said trunk line and for applying ringing currentthereto each time a connection is extended, an operatofis head set normally disconnected from said cord, means responsive to the connection of said cord to said trunk to answer a call for tripping the ring and for connecting said head set to said cord after the ring is tripped, and means for deactuating said last means and causing its reoperation responsive to the extension of a second call to said trunk line before said cord is disconnected therefrom after answering a previous call.

'7. In a telephone system, a trunk line i-neluding a ring control conductor and a re lease conductor terminating at an intercepting operators switchboard, an automatic switch and means controlled by a toll operator for operating said switch to connect with said trunk line to extend acall, a: first and a second relay for said trunk line, means in said switch for closing a circuit including said release conductor for said first relay to Cit-USU the same to operate, meanscontrolled by said first relay for closing, a holding cirh't including said ring control conductor for itself, and for closing a circuit including said release conductor for said second relay to cause it to operate, means controlled by said second relay for opening; the initial circuit of said first relay and for closing look ing' circuit including said release conductor for itself, a signal and a circuit therefor including normally open contacts on said second relay and normally closed contacts on said first relay. means in said switch controlled by the toll operator for opening the holding circuit of said first relayto cause the same to deenergize and close the circuit of said signal to cause the signal to operate and signal the intercepting operator, and means responsive to the answering of the all for opening the locking circuit of said second relay to cause said second relay to deonerg'ize and open the circuit of said signal.

8. In a telephone system, a trunk line including a ring control conductor and a release conductor terminating at an interc pting operators switchboard, an automatic itch and means controlled by a toll operator for operating said switch to connect with said trunk line to extend a call, a first and a second relay for said trunk line, means in said switch for closing a circuit including said release conductor for saidfirst relay to cause the same to operate, means controlled hy said first relay for closing a holding circult including said ring: control. conductor for itself. and for closing a circuit including said release conductor tor said second relay to rause it to operate, means tumtrolled by said second relay for opening the initial circuit of said first relay and for closing a locking circuit including said release conductor for itself, a signal and a circuit therefor including normally open contacts on said second relay and normally closed contacts on said first relay, means in said switch controlled by the toll operator for opening the a holding circuit of said first relay to cause the same to deenergize and close the circuit of said signal to operate and signal the m tercept-ing operator, means rcsponsiveto the answering of a call for opening the locking circuit of said second relay to cause said second relay to deenergize and open the circuit of said signal, a second signal at the toll operators position, and a third relay for said trunk energized in series With said first relay for controlling the operation of said second signal.

9. In a telephone system, a trunk line a switch and means for operating it to connect with said trunk line to extend a call, a first and a second relay for said trunk line, means in the switch for closing an initial circuit for the first relay to operate the same, means controlled by the first relay for closing a holding circuit for itself and for closing an initial circuit for the second relay, means controlled by the second relay for closing a holding circuit for itselt and for opening the initial circuit for the first relay,

a signal and. a circuit thel'e'tor inrludi ng normally open contacts on the second relay and normally closed contacts on the first re 1 means in the switch operahle at will for opening the holding circuit of the first relay to cause the same to deencrgiae and close the circuit of the signal, a cord circuit and means fer connecting it to the trunk line to answer the call, third relay for said trunk and means for operating it when the cord is connected tothe trunk to open the holding circuit of the second relay, and separate means for maintaining the third relay operated after the cord circuit is disconnected from the trunk to prevent the first and the second relay from reoperating.

In Witness whereof, I hereunto subscribe my name this 22d day of Jane A. D. 1921 THOMAS F. CRO CKER, 

